The present invention relates generally to a method and a device for controlling a multiplexed device. “Multiplexed display device” or more simply “multiplexed display” means, within the scope of the present description, a display device with multiple lines, i.e. a display device having a number of display lines greater than one, and which is controlled by multiplexing. “Multiplexing” means here that the display control signals are multiplexed over time. One will also speak of “dynamic” display.
The present invention applies to any type of multiplexed display, whatever its size. In particular, the present invention advantageously applies to multiplexed liquid crystal displays (LCD).
With reference to FIG. 1, there is illustrated a conventional dynamic display device 10. The display illustrated typically includes a first display section 10A and a second display section 10B. This display 10 is of a conventional type found for example in cellular telephones. The first display section 10A is thus a display section including predefined symbols, for example symbols intended to indicate the reception level of a cellular telephone, the battery autonomy, the arrival of a call, the time, or any other information which is typically permanently displayed on the display when the apparatus is activated. The second display section 10B is typically a matrix type display section for displaying alphanumerical and/or graphic data such as the number of a caller, a short message, etc. The first and second display sections are typically physically interconnected so as to form only one composite display including a section of symbols and a matrix section for displaying alphanumerical messages.
The display illustrated in FIG. 1 thus typically has a set of segments or pixels arranged in lines and columns. In order to activate these segments and pixels, a plurality of line and column electrodes (not shown), are respectively coupled to lines and columns of the display. In the case of an LCD display, these line and column electrodes are for example disposed on opposite plates between which the liquid crystal layer is arranged. Voltages applied to the line and column electrodes combine to generate an electric field in a zone between the electrodes. This zone between the electrodes is called “pixel” or “segment” depending on the geometry of the zone. Thus, in the case of first display section 10A including the symbols, one will preferably speak of “segments”, whereas in the case of second display section 10B, one will preferably speak of “pixels”. Nonetheless, in both cases, the voltages applied to the line and column electrodes combine to selectively activate or deactivate pixels or segments of the display. By way of simplification, the term “pixel” will be used in the following description to indicate indiscriminately a pixel or segment of the display.
It will be understood that the terms “line” and “column” are used to indicate that the pixels are arranged in matrix form and are controlled by pairs of electrodes, each pixel being located at an intersection of a pair of line and column electrodes. In certain displays, these pairs of electrodes can however be called differently, for example by the terms “foreplane electrode” and “backplane electrode”. Within the scope of the present description, the terms “line electrode” and “column electrode” designate any type of electrode arrangement, including arrangements wherein the electrodes are not arranged in a linear manner. It will also be understood that the terms “line” and “column” do not necessarily imply that a line extends horizontally and that a column extends vertically. The terms “line” and “column” can thus perfectly well be interchanged.
The dynamic displays that have just been briefly presented, such as Liquid Crystal Displays (LCD), are frequently used in numerous battery-powered products, such as calculators, personal digital assistant, portable phones, electronic timepieces, etc. One significant advantage of such display devices is their relatively low power consumption allowing the products incorporating them to operate for a long time by means of their battery or to operate with batteries of smaller dimensions.
The current tendency is to produce efficient devices of small dimensions whose power consumption is reduced as much as possible. One way of saving energy in a device incorporating a dynamic display such as an LCD would consist in entirely cutting off the power supply to the display pixels which are in standby mode or which are not otherwise being used. It has been realised however in practice that it is not possible to cut off the power supply to the pixels entirely. In practice, the pixels, in particular the pixels of an LCD type display typically have to be controlled by a alternating control signal of zero continuous component, even when the pixels are in the “off” state. If the control signal included a non-zero continuous component, this could result in residual polarisation of the display which would make the latter non-operational.